The invention relates to a method and apparatus for the continuous manufacture of extruded materials in general and more particularly to such a method in which feeding forces are reduced.
Such a method and apparatus for the continuous manufacture of extruded material such as chip board, plastic board and similar materials, in which the material to be pressed is conducted between endless forming bands which co-circulate in a pressing section is described in DE OS No. 21 577 746, for example. The forming bands circulate in the feeding direction of the extrusion and extend over the width of the extrusion. Pressure and optionally heat are introduced through the forming bands into the material.
The band presses may be of different design. A first possibility is that according to DE-OS No. 21 57 746, in which the material to be pressed is guided between forming bands of sheet steel which are supported on the back side via co-circulating roller chains. German Pat. No. 936 718, on the other hand, discloses a band press in which co-circulating steel bands are supported via co-circulating plate chains which have rolls on the back side which roll against support tracks. Band presses, in which the forming band itself consists of individual strip-like plates which are linked together along a line extending cross-wise to the extrusion can also be used. Forming bands which are supported by means of continuous rolls extending across the width of the extrusion as well as forming bands which are guided past a support structure with sliding friction also can be considered in this type of apparatus.
The present invention is directed to the solution of a problem which arises if especially thick plates or blocks are to be produced on a press of this type, in which the dimensions of the sides of the rectangle forming the cross section are of the same order of magnitude. For, in the manufacture of such especially thick chip boards or chip blocks, the material is squeezed out from between the forming bands at the sides under high pressure if, on a normal chip board press, the necessary, very high chip piling is run into the pressing section. In order to prevent this it is absolutely necessary to provide seals at the sides of the press in these cases, in order to keep the cross section of the material extrusion which is being formed rectangular.
While these seals can theoretically be designed as co-circulating seals, the effort connected therewith, especially if band presses with variable thickness of the material extrusion being produced are involved, is so great that practically only a stationary seal can be considered for economic reasons. In a mass of chips quasi-hydrostatic conditions prevail under high pressure, so that a considerable part of the pressure to be transmitted to the forming band is also found as a pressure acting in the transverse direction against the seals, and the friction to be overcome by the material extrusion or the band press is thus very considerable.
The feeding forces are transmitted, in many of the known press designs, especially of those according to DE-OS No. 21 57 746, through the forming bands. These are deflected over drums at the ends and the bending stresses due to the deflection are further superimposed on the pure tensile stress in the deflection region. The total stress resulting therefrom exceeds the permissible material stresses in the forming band if stationery seals are used.
It is an object of the present invention to develop a method and apparatus of the type discussed above in which the feeding forces to be transmitted by the forming bands are reduced.